National mineral assessment tract AK-SW11 (Porphyry Cu, BC-Ak type)

Tract AK-SW11
Geographic region Southwestern, AK
Tract area 28,279sq km
Deposit type Porphyry Cu, BC-Ak type
Deposit age Cretaceous - Tertiary


Explained by Marti L. Miller and Bruce M. Gamble
On the choice of deposit models
This tract is permissive for porphyry Cu (Cox, 1986a), BC-Ak type porphyry Cu (Menzie and Singer, 1993), porphyry Cu, skarn related (Cox, 1986c), and porphyry Cu-Mo (Cox, 1986b) deposits based on presence of felsic to intermediate plutons (Patton and others, 1994), and the occurrence of numerous similar or related deposit types. St. Matthew Island is also considered permissive for porphyry Cu type deposits on the basis of permissive host rocks.
On the delineation of permissive tracts
The geology of the area is poorly known, but several apparently high-level felsic plutons occur in the region, and others could be present at shallow depths. The presence of permissive host rocks is the primary basis for the areal delineation of this tract. On St. Matthew Island, Patton and others (1975) mapped a small Tertiary granodiorite body; the possibility of porphyry-type mineralization here cannot be ruled out on the basis of available information.
Important examples of this type of deposit
A molybdenum prospect at Molybdenum Mountain. (Russian Mission quadrangle), described by Hoare and Cobb (1977), could be related to porphyry Cu or porphyry Cu-Mo occurrences.
On the numerical estimates made
Because of the lack of detailed geologic information, no estimates of the number of undiscovered deposits have been attempted.
Cox, D.P., 1986a, Descriptive model of porphyry Cu, in Cox, D.P. and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 76.
Cox, D.P., 1986b, Descriptive model of porphyry Cu-Mo, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 115.
Cox, D.P., 1986c, Descriptive model of porphyry Cu, skarn-related deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 82.
Hoare, J.M., and Cobb, E.H., 1977, Mineral occurrences (other than mineral fuels and construction materials) in the Bethel, Goodnews, and Russian Mission quadrangles, Alaska: U.S. Geological Survey Open-file Report 77-156, 98 p.
Menzie, W.D., and Singer, D.A., 1993, Grade and tonnage model of porphyry Cu deposits in British Columbia, Canada, and Alaska, U.S.A.: U.S. Geological Survey Open-file Report 93-275, 8 p.
Patton, W.W., Jr., Box, S.E., Moll-Stalcup, E.J., and Miller, T.P., 1994, Geology of west-central Alaska, in Plafker, George, and Berg, H.C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-1, p. 241-269.
Patton, W.W., Jr., Miller, T.P., Berg, H.C., Gryc, George, Hoare, J.M., and Ovenshine, A.T., 1975, Reconnaissance geologic map of St. Matthew Island, Bering Sea, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-642, scales 1:125,000 and 1:250,000.

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